1. Field of the Invention
The present invention pertains to high load transmission chains and, particularly pertains to a high load transmission chain made completely of non-metallic materials.
2. Discussion of Prior Art and Problems
The substitution of non-metallic for metallic materials is often desirable for many well-known reasons too numerous to entail. Making a choice of a precise material for a particular application from the great many materials which are available, however, is extremely complex since the lightness, various moduli, and other physical characteristics of non-metallic materials pose severe and often unexpected problems to the applications engineer. The problem is no less severe to the engineer wishing to substitute non-metallic materials for chain. Rigid constraints are placed upon the selection, for example, by the environment in which the chain is to be used and the magnitude of the loads acting upon the chain.
Numerous patents have issued that describe chains at least a part of which are made from non-metallic materials. For example, U.S. Pat. No. 3,281,121 describes a chain made from an electrically non-conductive material such as a plastic marketed under the name of "Delrin." The patentee readily admits that while it is preferable that the side plates and pins are metallic, each could be made of a dielectric material also. Unfortunately, the patentee also acknowledges that the pin must be substantially larger to obtain the same strength characteristics of metal components. Obviously, a large load on a chain with a dielectric pin would cast doubts on the viability of a dielectric pin, particularly in sustained operation. Consequently, it is generally preferred to use a metallic pin even when employing non-metallic links.
Another patentee in U.S. Pat. No. 3,127,980 discloses a drive chain comprised of plastic material, primarily for use with conveyor belts for bakery products. The desirability of using a chain that would not tend to contaminate the product is apparent. The links are made of a plastic material. The patentee's chain did not employ pins but the links thereof were connected by bosses and holes alternating in each link end. The resilience of the material was utilized to spread the side arms of the links to place the bosses in the hole. This patent again illustrates the practice of using non-metallic chains, but only when large loads are not expected.
Solutions of the problems as set forth by, for example, the patents discussed above are not readily transferrable to other problems confronting those skilled in the art of manufacturing and using chain. In the present situation, it was desired to fabricate a chain of light weight material which would function as well as metallic counterparts under heavy loads in environments hostile to metals, ie. corrosive solutions and high humidity. Long service life was definitely needed. Non-reactive plastic materials appeared to be the partial answer, but would have to withstand the expected large loads. Yet the known prior art was devoid of any practical answers to the problems created by the high load requirements operating in corrosive environments. It was with the above constraints in mind that applicants sought to provide a chain which at once would stand high loads and operate in environments under which cast chain would deteriorate.